1. Field of the Invention
The present invention relates to image forming devices and, more particularly, to laser-based image scanning devices having a plurality of lasers.
2. Description of the Related Art
FIG. 1 is a schematic diagram of a laser beam scanning unit. The laser beam scanning unit 2 includes a surface emitting semiconductor laser array 4 having a plurality of light emitting lasers 6 two-dimensionally disposed thereon. The intensity of the laser beams produced by the lasers 6 is discretely controlled by a control unit 8. Laser beams emitted from the lasers 6 are collimated by a collimator lens 10 to produce laser beams with a predetermined beam diameter. The laser beams then strike a facet of a rotating polygon mirror 12 and are directed through an objective lens 14 and onto an image bearing member 16. The laser beams striking the image bearing member 16 form spots 18 along scan lines 20 produced by rotating the polygon mirror 12. Further, details on the laser beam scanning unit shown in FIG. 1 are described in European Patent Publication 0544002 A1.
Conventionally, the lasers within an array of lasers are all designed to have the same intensity output for a given driving voltage. However, when actual manufacturing of the semiconductor lasers takes place, differences in intensity performance occur among the lasers within the array. As a result, the lasers within an array will each have different intensity responses to a given driving voltage. The different intensity responses will result in a lack of uniformity among the lasers of the array. As a consequence, for a given applied driving voltage, the spots produced by the various lasers in the array will have different sizes. This causes image quality to suffer because precise control of spot size amongst an array of lasers is unavailable which makes streaks and other defects likely to occur in a scanned or printed image.
Thus, there is a need to precisely control the size of spots produced by an array of lasers.